forward_child: 4 branch streams fork after h_s2, join before loss aux_child: IQL/IQN/attention on parallel streams Uses CU_STREAM_CAPTURE_MODE_RELAXED with fork-join events as graph edges Existing branch_streams[4] + events in batched_forward.rs ready to activate Target: <40s epochs (from <80s Phase 1) Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>